A process has been proposed for producing a granular detergent composition containing a nonionic surfactant which comprises mixing the nonionic surfactant with a detergent slurry and spray-drying the resulting mixture. This process, however, not only requires great expense for facilities but also uses great amounts of energy. Further, it has a possibility of causing thermal decomposition of the nonionic surfactant during the drying step, which entails problems such as generation of pollutants, reduction of the content of the nonionic surfactant, changes in the properties of the active agent and the like. In order to work out such problems, it is necessary to limit types and contents of nonionic surfactant as disclosed, for example, in JP-A-61-85499 (corresponding to U.S. Pat. No. 4,652,391) or to further blend a charge-transfer agent as disclosed, for example, in JP-A-56-22394 (corresponding to U.S. Pat. No. 4,298,491). The term "JP-A" as used herein means an "unexamined published Japanese patent application".
JP-B-60-21200 (corresponding to DE 2,707,280) proposes a production process in which builder base beads are prepared by spray-drying and a nonionic surfactant is supported on the base beads. The term "JP-B" as used herein means an "examined Japanese patent publication". However, since this process requires an anhydrous phosphate builder salt as a base material, application thereof is restricted only to the production of phosphorous-containing detergents, so that phosphorous-free detergents could not be produced in the process. Further, it requires complicated handling for the preparation of base beads having porous surfaces and internal skeleton structures.
JP-A-61-21997 (corresponding to U.S. Pat. No. 4,427,417) discloses a process for the continuous production of a granular detergent free from caking during a prolonged period of storage which comprises hydrating and swelling a washing active salt using an agglomerater or the like, stirring the resulting swelled salt in a closed vessel, impregnating thereto a nonionic surfactant, an anionic surfactant and the like and then drying the resulting mixture. This process, however, requires a drying step after the granulation because the surfactant is impregnated into the hydration-swelled granular agglomerates of the washing active salt, thus it is too complicated. Further, since an amount of the nonionic surfactant which can be incorporated in the granular detergent depends upon the characteristics of the granular agglomerate, a granular agglomerate of high oil absorbing property should be prepared to increase the amount of the nonionic surfactant. However, when a granular agglomerate of high oil absorbing property is to be prepared, an amount of a non-hydrating washing active salt would be increased, so that an undesirable result is caused. Thus, compositions of granular detergents which can be produced in this process narrowly restricted. Furthermore, this process requires complicated operations (e.g., hydration and drying conditions) for the detergent production.
JP-A-3-26795 (corresponding to U.S. Pat. No. 5,024,782) discloses a process for producing a granular detergent having excellent fluidity, solubility and dispersibility which comprises forming zeolite agglomerates from a zeolite and a filler with using a water-containing binder in an agglomerate forming apparatus, further forming detergent agglomerates from the zeolite agglomerates and a detergent composition containing a surfactant, and then drying the resulting detergent agglomerates. This process, however, have disadvantages in that it requires complicated handling for the detergent production because at least five operation steps are necessary to obtain the detergent agglomerate, and that the zeolite agglomerate must be formed, thus the granular is apt to encounter a narrow compositional restriction.
JP-A-62-263299 discloses a process for the production of a granular detergent composition which comprises forming a solid detergent by uniformly kneading a nonionic surfactant and a builder and then crushing the solid detergent.
However, a granular detergent having good fluidizability is hardly obtained by this process, and a large amount of undesirable fine powders is co-produced in this process. Further, a zeolite and a light sodium carbonate should be employed in the granular detergent in an amount of 50 to 80% by weight in total, thus the detergent suffers from the restrictions of the composition.
JP-A-61-89300 discloses a process for producing nonionic surfactant-containing granules which comprises mixing a water-soluble powder and a powdery silica, spraying a nonionic surfactant onto the mixture, then adding thereto a zeolite or sodium carbonate powder. However, in this process, the granules are prepared by rolling and granulating using a drum type granulator of which granulation is effected with a rotating drum, a nonionic surfactant-containing granules of high bulk density cannot be obtained.